The invention relates generally to connection assemblies for electronics and, more particularly to a fiber-optic cable system which provides a connection between a fiber optic cable and an electronic device. The system of the invention provides high precision interconnections which makes it particularly well suited for microelectronic device packages.
Because of their inherent capability of transmitting more data than any comparably sized electrical wire, fiber optic cable transmission lines have become more widely used in various electronic applications including those utilizing microelectronic components. Since fiber optic cables do not produce electromagnetic interference and are not susceptible to radio frequency interference, they have become more desirable in computer systems and avionic systems and many other types of systems in which noise interference can cause malfunction thereof. Moreover, fiber optic cable transmission systems have an additional advantage of having lower power requirements than electrical wire transmission lines of comparable data transmission capabilities. However, fiber optic cable transmission systems have the disadvantage of requiring precise alignment of their connections in order to function properly. This important disadvantage of fiber-optic cable systems has to a certain degree obviated the advantages such systems have and prevented them from more widespread use.
Current electronic packaging of devices are now confronting the problem of input and output bounding wherein the number of inputs and outputs needed is the most important factor determining the size of the device package. For example, it is now common that there are 500-700 I/O bald grid arrays in midrange personal computers. There are also higher I/O counts in high end computers as well as in data fusion or graphics applications. However, using such high pin counts has a significant drawback in that soldering the many pin connections has a certain element of risk as it takes only one failed solder joint to cause a system failure. As a result designers have investigated the use of optical interconnections between these large package devices including FPGAs, microprocessors, memory devices etc.
Current fiber-optic systems use discrete devices to convert the light pulses from the fiber-optic cable into electrical signals. The signals are then conducted to the next device using a printed circuit board to connect to high count I/O packages. The signals are then demultiplexed down to a lower data rate required by the lower speed low-power technologies. As a consequence, the I/O increases to maintain the data rate. I/O power is a significant contributor to the overall power consumption of the integrated circuit.
An optical interconnections system for electronic devices has the important advantage of enabling high data transfer between microelectronic devices. However, the development of such a system involves various problems. Such systems would require that a microelectronic package be used to mount the VCSEL transmitters and detectors as well as the fiber optic connector body onto. In addition, very precise alignment of the fiber-optic connector body and the electronic device base is required. This alignment requirement is on the order of approximately 5 to 10 microns for multimode fiber. Some applications would desire a fixed connection whereas other applications would desire a removable connection.
Prior art systems used in applying photo resistors to semiconductor wafers have utilized an alignment method. In the fabrication of the semiconductor substrates a holographic system using an infrared light is used to backlight alignment patterns on a substrate fabricated in the wafer. The substrate is transparent to the infrared light and thus can be detected by a holographic imaging and detection system to automatically align the wafer.
Some prior art approaches to providing optical communication for electronic devices involve mounting the electronic devices in a transparent substrate. Ultra-thin silicon-on-sapphire CMOS technology produces circuitry extremely well suited for optical communications functions on a transparent substrate. The silicon and sapphire process allows for flip chip bonding of optical electronic devices and to CMOS circuitry to build flipped optical chip and UTSi (FOCUTS) modules. Flip chip bonding eliminates the wire bond inductance between driving/receiving circuits and the OE devices which becomes problematic at data rates greater than 2.5 Gbps. The flip chip bonding also reduces the number of discrete chips that must be handled, packaged and aligned in the final module thereby reducing manufacturing costs. Because of the isolating substrate and the elimination of the substrate parasitic effects, the UTSI process produces high-performance CMOS circuitry requiring less power than bulk Si CMOS circuitry. In the current 0.5 micron UTSI process, modulation rates greater than 5 Gigahertz are achievable. UTSI with 0.25 micron features will be available allowing greater than 10 Gigahertz modulation. Additional byproducts of the UTSi are the availability of multi-threshold transistors in the EEPROM devices. Even with these enhancements, the standard semiconductor tools used for CMOS are also used for designing simulation fabrication packaging and testing UTSi. The fabrication process yield is comparable to bulk SI and the processed wafer cost is much less than competing high-performance technologies such as GaAs, BiCMOS and SiGe. The isolating substrate allows for mixed signal integration, as demonstrated in prior art wireless products.
Optical data communication products such as VCSELs are very cost effective due to wafer scale processing and testing and standard IC handling. Their optical properties also allow more tolerance on alignment thereby being preferable in less stringent packaging techniques. Similar cost reductions are offered by flip chip bonding OE devices to UTSi and packaging in a method compatible with electronic and fiber optic technologies.
The UTSi technology applied to optical transmitter/receiver modules allows a high degree of functional integration within the module. The non-conducting sapphire substrate of the UTSi provides a high degree of isolation between mixed signal circuits, enabling the integration of high-performance transmitters, receivers and other sensitive analog circuitry with digital circuitry. The fact that UTSi uses standard CMOS CAD tools allows easy importing of standard digital CMOS function block. Examples of key telecom blocks are digital modulation coding, your correction coding, routing, deskewing, equalization, ADC/DAC, multiplexing and demultiplexing circuitry. This integration ultimately reduces the cost and increases performance as compared to board level integration. Additionally, the UTSi process has the capability of multilevel threshold transistors and EEPROM devices. Multilevel transistors give the circuit designer added flexibility to increase performance and reduce power consumption.
EEPROM devices integrated with the drivers and logic circuitry reduces board level complexity and thereby provides another cost savings. EEPROM memory can be used for several functions including storage of trim values to equalize the drive bias on VCSEL devices across the parallel channels, hardware node address information for networking, network fault codes, error correction coefficients, initialization and training sequences for link startup.
The use of VCSELs to emit light through the UTSi substrate provides several advantages related to device packaging. Mating the fiber coupling assembly directly to the sapphire substrate creates a physically compact module. The transparent substrate enables alignment between marks on the UTSi and the fiber coupling assembly. Integration of an optical photodetector fabricated in the UTSi process for automated power control provides further advantages. The detector picks off a small percentage of the light to control the output optical power, an essential function in optical links. In addition, this through substrate design allows integration of microlens arrays directly etched into the sapphire or fabricated onto another type of substrate (such as glass) or contact mounted on the sapphire.
It is a principal object to the present invention to provide a connector system for an electronic device which enables optical signal transmission thereto and therefrom.
It is also an object of the present invention to provide a connector system for an electronic device which utilizes optical connections at the electronic device terminals for providing single point ground connections for the electronic device as well as electronic units and subsystems associated therewith.
It is also an object of the present invention to provide a connector system for connecting a fiber-optic cable plug connector to an electronic device capable of high precision alignment and attachment of a fiber-optic cable terminus connection thereto.
It is also an object of the present invention to provide a connector system for connecting a micro fiber optic cable to a micro electronic device to a micro electronic device capable of high precision alignment and attachment of a micro fiber optic cable terminus connection thereto.
It is also an object of the present invention to provide a connector system for connecting a fiber-optic cable plug connector to an electronic device having a minimal number of components thereof.
It is an object to the present invention to provide a connector system for connecting a fiber-optic cable plug connector to an electronic device which has a minimal number of electrical transmission lines for minimal power consumption.
It is an object of the present invention to provide a connector system for connecting a fiber-optic cable plug connector to an electronic device which utilizes a high precision optical alignment system providing signal transmission capability without signal loss or degradation.
It is an object to the present invention to provide a connector system for connecting a fiber-optic cable plug connector to an electronic device which has a minimal number of I/O pin connections for minimal power consumption and maximal data transfer rates.
It is an object of the present invention to provide a connector system for connecting a fiber-optic cable plug connector to an electronic device which integrates the transmitter, detector and fiber-optic cable plug into the electronic device package.
It is an object of the present invention to provide a connector system for connecting a fiber-optic cable plug connector to an electronic device which utilizes a substrate for containing the electronic device as well as the electronic units and transmission lines associated therewith.
It is an object of the present invention to provide a connector system for connecting a fiber-optic cable plug connector to an electronic device which is relatively inexpensive.
It is an object of the present invention to provide a connector system for connecting a fiber-optic cable plug connector to an electronic device utilizing optical interconnections for minimizing susceptibility to EMI and RFI.
The system of the present invention provides a connection between an optical transmission line and an electrical subsystem such as an electronic device and a fiber optic cable in order to interconnect various desired systems via the fiber optic cable interconnect. A modern electronic device is typically connected to a transmitter and detector for carrying signal data to and from the device. Essentially, the system of the invention specifically provides an interface between the terminus of the fiber optic cable and the transmitter and detector elements. The system of the present invention includes a base and a plug connector in which the fiber optic cable plug and terminus are located. The plug connector has a receptacle for receiving the fiber optic cable plug. The base has a substrate which contains the electronic device. The base also incorporates a converter for converting an electrical signal to an optical signal or for converting an optical signal to an electrical signal.
Transmitting data streams through fiber optic cable increases data transmission rates to a level that is significantly higher than what current printed wiring board technologies can support. For example, a printed wiring board made from epoxy glass material has variations in dielectric constants which make high-speed data communications difficult due to parasitic losses in the material. The higher the dielectric constant of the material the lower the maximum signal speed thus requiring controlled impedance structures typically under one Gigahertz. Polyimide glass materials have a more uniform dielectric constant that allows controlled impedance structures to support higher transmission speeds typically under two gigahertz. Using the more exotic printed materials made from Teflon derivatives will allow increased transmission speeds in the one to thirty gigahertz range. However, these types of printed wiring boards are not suitable for high layer count construction. However, optical transmission has been demonstrated to transmit ten GBit/s without any degradation in signal due to parasitic losses and noise.
Relatively low power consumption is realized by using prior art semiconductor device packaging technology using sapphire substrate. Other types of transparent mediums may be used in the substrate, but an added advantage of using sapphire is that there is no capacitive loss. The sapphire is also transparent thus allowing the VCSEL and detectors to be flip chip mounted onto the interior surface of the device while facing out toward the fiber optic cable. The sapphire is also very hard and durable allowing it to withstand handling without damaging the optical window to the VCSEL or detector. It also has the inherent characteristic of radiation hardness.
In order to produce the desired interconnections between the electronic device and the fiber optic cable plug connector, a high degree of accuracy in aligning the plug connector to the electronic device is required. The alignment method of the present invention provides alignment to within a five to ten microns positional tolerance. The positioning method of the present invention accurately, quickly and efficiently aligns the plug connector onto the base in which the opto-microelectronic device is mounted. When sapphire is used as a transparent medium, its beneficial characteristic of functioning as an optical waveguide results in light being channeled through the substrate to the area which has an alignment means used to enable determination of the position of the substrate in relation to the plug. The optical waveguide method is similar to that used in an automobile holographic center mount stoplight system and in other automobile holographic displays. The method used in automotive applications is based on that originally developed in heads up display systems for fighter aircraft.
The system of the present invention utilizes a trapped beam lighting technology to accomplish the alignment. Due to the particular optical waveguide characteristics of sapphire, light rays are refracted by the substrate and are reflected from the sides of the substrate into the interior of the substrate so that they propagate through the medium rather than passing out through the sides of the substrate. The light is injected into the side of the substrate at an angle which induces refraction of the light into the interior of the substrate and promotes internal light reflections between the sapphire/air interface at the sides of the substrate. This allows the plug connector to be aligned with either packaged or unpackaged substrate. The light is from a remote source using a fiber optic cable to direct the light into the substrate. The input angle of the light beam is selected so that it is refracted out of the substrate and through the alignment determination area with only a minor angular change. The theory and calculations of light ray reflection and refraction are defined by Snell""s Law. Light from the light source is essentially trapped inside the substrate by total internal reflections from the air/sapphire interface at the various outer surfaces of the substrate.
The positioning and placement of the plug connector onto the opto micro electronic device is a several step process involving alignment of the plug connector with the substrate and secure attachment of the plug connector to the base at the substrate. This operation requires an automated positioning system consisting of a vision system for viewing the alignment images to enable determination of the position of the components to be joined and a position adjustment system for horizontal rotational and vertical linear movement to bring these components into the desired position of alignment.
The vision system used in alignment of the plug connector to the base utilizes one or more cameras to view alignment images. Essentially, the cameras receive the light passing out of the substrate and through the alignment pattern which produces the alignment images. The cameras transmit image data to a microprocessor which compares the data to reference image data. The microprocessor determines whether there is alignment and, if not, calculates the positional change of the plug relative to the base required to bring the structures into the desired alignment. The alignment system may utilize an alignment pattern in the substrate in conjunction with an alignment feature on the plug or simply utilize a holographic image from the substrate (with or without an alignment feature on the plug) to determine position and orientation of the viewing cameras/and thereby the plug in relation to the three dimensional image produced by the hologram in the substrate.
A physical translation system is utilized to move the plug vertically and to move the base horizontally. This vertical translation system is used to bring the structures into alignment in response to operational commands from the microprocessor and also move the structures into the desired degree of proximity. The translation system utilized has a repeatability of plus or minus five microns.
Once the base and the plug connector are in mutual alignment and in the desired degree of proximity to each other, the structures are secured together. This securement process preferably includes adhesive injected into the separation gap between the base and the plug. Alternatively, instead of bonding, a mating pin and hole structure may be machined into appropriate portions of the plug and base for removable connection thereof.
The system hardware is expected to provide a data flow rate of two and one-half Gbit/s. However, data flow rates can be increased to ten Gbit/s by decreasing the feature size of the electronic device to 0.25 microns.
In the commercial network market the incorporation of fiber optic cables that are integrated directly into optical electronic devices will enable the reduction in volume and cost and increase the bandwidth of the existing fiber based networks. Taking this one step further, this proposed fiber optic connector system and opto packaging assemblies become optically linked.
Additional improvements over the integration of opto and PGA devices include fitting an entire array or a variety of devices with the opto front end, enabling the creation of an integrated optical network for spacecraft. The devices needed to realize this include analog digital converters, microprocessors, memory modules and multichip modules.
It can be expected that as the space infrastructure continues to develop and on-orbit assets are deployed there will be a need to perform repair, refurbishment and refueling. Repair is self-explanatory. When an orbital asset has a module or subsystem that fails it will be far easier to send a microsat with a needed subsystem to become a permanent part of the asset. Refurbishment occurs when the entire subsystem is taken off line and replaced by a new subsystem brought to the assets by the microsat. By utilizing a fiber optic connection between the two craft the chances for any static electricity to cause harm during the docking process is mitigated.
In another application, the sensor and data fusion engine (SAFE) is used to analyze external data and relay it in a usable form by the vehicle""s controlled guidance system or relay it back to the war fighter for further analysis or use. The reliability of the SAFE is a critical factor in performing its mission. To this end the SAFE must be protected from both natural and man-made phenomena. One method is to isolate the SAFE by using opto isolators on all I/O lines. This is easily accomplished by using an opto-FPGA as the I/O front end.
Another application relates to threat awareness on board spacecraft which is typically performed by a number of sensors to detect the external application of non-natural energy sources such as laser, high-energy and kinetic sources. The opto connection system of the present invention provides a robust means of data transfer from the sensors to the threat analysis computer to prevent any stray electrical noise pickup. This prevents any natural energy sources from creating a ghost signal to the threat analysis computer and interpreting the ghost signal as an attack. On the other side, a robust data transmission system will allow the spacecraft to continue to operate when an assault attempts to disrupt internal data flow.
The connector system of the present invention thus provides a means for aligning and attaching a fiber optic cable connector to an electronic device with a very high degree of precision. In addition, the system of the present invention has the desirable features of enabling such alignment and attachment to be performed on component structures which include micro electronics. The utilization of microprocessors enables the alignment to be an automated process. After the component structures are properly aligning they are either permanently securely attached with the plug securely attached to the plug connector, or the plug may be removably attached to the plug connector via appropriate pin and hole structures. The connector system advantageously provides an optical interconnect to the transmitter and detector elements of an electronic device interface that improves system performance through increased data transmission rates, lower power consumption, and opto isolation of I/O that enables a single point ground connection between subsystems that further improves performance. Essentially, the system provides integration of optical and electrical converters with an electronic device and with a fiber optic cable plug connector producing an electronic device assembly that is able to optically interconnect with other electronic devices and systems.